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Date: Thu, 10 Nov 2022 16:20:17 -0800 From: Stanislav Fomichev <sdf@...gle.com> To: Martin KaFai Lau <martin.lau@...ux.dev> Cc: Toke Høiland-Jørgensen <toke@...hat.com>, ast@...nel.org, daniel@...earbox.net, andrii@...nel.org, song@...nel.org, yhs@...com, john.fastabend@...il.com, kpsingh@...nel.org, haoluo@...gle.com, jolsa@...nel.org, David Ahern <dsahern@...il.com>, Jakub Kicinski <kuba@...nel.org>, Willem de Bruijn <willemb@...gle.com>, Jesper Dangaard Brouer <brouer@...hat.com>, Anatoly Burakov <anatoly.burakov@...el.com>, Alexander Lobakin <alexandr.lobakin@...el.com>, Magnus Karlsson <magnus.karlsson@...il.com>, Maryam Tahhan <mtahhan@...hat.com>, xdp-hints@...-project.net, netdev@...r.kernel.org, bpf@...r.kernel.org Subject: Re: [xdp-hints] Re: [RFC bpf-next v2 06/14] xdp: Carry over xdp metadata into skb context " On Thu, Nov 10, 2022 at 3:58 PM Martin KaFai Lau <martin.lau@...ux.dev> wrote: > > On 11/10/22 10:52 AM, Stanislav Fomichev wrote: > >>> Oh, that seems even better than returning it from > >>> bpf_xdp_metadata_export_to_skb. > >>> bpf_xdp_metadata_export_to_skb can return true/false and the rest goes > >>> via default verifier ctx resolution mechanism.. > >>> (returning ptr from a kfunc seems to be a bit complicated right now) > > What is the complication in returning ptr from a kfunc? I want to see if it can > be solved because it will be an easier API to use instead of calling another > kfunc to get the ptr. At least for returning a pointer to the basic c types like int/long, I was hitting the following: commit eb1f7f71c126c8fd50ea81af98f97c4b581ea4ae Author: Benjamin Tissoires <benjamin.tissoires@...hat.com> AuthorDate: Tue Sep 6 17:13:02 2022 +0200 Commit: Alexei Starovoitov <ast@...nel.org> CommitDate: Wed Sep 7 11:05:17 2022 -0700 bpf/verifier: allow kfunc to return an allocated mem Where I had to add an extra "const int rdonly_buf_size" argument to the kfunc to make the verifier happy. But I haven't really looked at what would happen with the pointers to structs (or why, at all, we have this restriction). > >> See my response to John in the other thread about mixing stable UAPI (in > >> xdp_md) and unstable BTF structures in the xdp_md struct: I think this > >> is confusing and would prefer a kfunc. > > hmm... right, it will be one of the first considering the current __bpf_md_ptr() > usages are only exposing another struct in uapi, eg. __bpf_md_ptr(struct > bpf_sock *, sk). > > A kfunc will also be fine. >
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